1. Field of the Invention
The present invention relates to an air volume control module for controlling the rotational speed of the blower of a vehicular air conditioning apparatus.
2. Description of the Related Art
Vehicular aid-conditioning systems include a blower unit and a cooling/heating unit. Air delivered from the blower of the blower unit is adjusted in temperature by the evaporator and heater of the cooling/heating unit and introduced as conditioned air from air outlets into the passenger compartment of the vehicle.
The blower is rotated by a motor whose rotational speed is controlled by an air volume control module for use with the vehicular air conditioning apparatus, as disclosed in Japanese Laid-Open Patent Publication No. 2005-289243.
One known air volume control module of the type described above is shown in FIGS. 7 and 8 of the accompanying drawings. As shown in FIGS. 7 and 8, the air volume control module, generally denoted by 1, comprises a circuit board 2 including a control circuit, a heat sink 3 on which the circuit board 2 is mounted, and a base housing 5 surrounding a portion 4 of the heat sink 3 on which the circuit board 2 is mounted. The portion 4 will hereinafter be referred to as “board mount 4”.
The base housing 5 is generally made of a resin material and has an insertion opening 6 defined in one end thereof for the insertion therein of the heat sink 3. The heat sink 3 has a support base 7 disposed on the board mount 4 and a plurality of fins 8 mounted on the support base 7. The support base 7 is wider than the insertion opening 6. When the support base 7 is secured to the base housing 5 with the board mount 4 inserted in the insertion opening 6, the heat sink 3 is supported on the base housing 5 with the fins 8 projecting therefrom (see FIG. 8).
The board mount 4 includes a pair of parallel support plates 9, 10 (see FIG. 7) extending parallel to each other away from the support base 7. The circuit board 2 is firmly mounted on the parallel support plates 9, 10. Four terminals 11 through 14 are joined to the circuit board 2 and extend away from the board mount 4. When the board mount 4 is housed in the base housing 5, the terminals 11 through 14 project into a terminal protector 36 of the base housing 5. In FIG. 7, the terminals 12, 14 are positioned behind the respective terminals 11, 13 and hence concealed from view.
A power transistor, not shown, is mounted on the circuit board 2. The terminals 11, 12, the terminal 13, and the terminal 14 are electrically connected respectively to the drain, gate, and source electrodes of the power transistor. A capacitor 15 is also mounted on the circuit board 2.
A plurality of resistors, not shown, are also mounted on the circuit board 2. The power transistor, the capacitor 15, and the resistors are electrically connected, making up a control circuit for controlling the rotational speed of the motor.
The base housing 5 has a pair of through screw holes 16, 17 defined therein. The heat sink 3 includes a pair of internally threaded legs 18, 19 disposed adjacent to the respective parallel support plates 9, 10 and positioned diagonally opposite to each other across the heat sink 3. Screws 20, 21 are inserted respectively through the through screw holes 16, 17 and threaded respectively into the internally threaded legs 18, 19, thereby fastening the base housing 5 to the heat sink 3.
The air volume control module 1 thus constructed is installed at a given position in the vehicular air conditioning apparatus, and an electric power source is electrically connected to the terminals 11 through 14.
The base housing 5 has an end flange having a triangular end and a trapezoidal end which are opposite to each other. When an attempt is made to install the base housing 5 in a wrong orientation in the vehicular air conditioning apparatus, the triangular end of the end flange of the base housing 5 physically interferes with a certain surface of the vehicular air conditioning apparatus, preventing the base housing 5 from being installed in the vehicular air conditioning apparatus. Consequently, the base housing 5 can be installed in the vehicular air conditioning apparatus only when the base housing 5 is properly oriented with respect to the vehicular air conditioning apparatus.
The base housing 5 is fastened to the heat sink 3 by the screws 20, 21. However, the fastening process is tedious and time-consuming to perform because it is necessary to position the screws 20, 21 with respect to the through screw holes 16, 17 and turn the positioned screws 20, 21 to tighten them in the internally threaded legs 18, 19.